CMS-PAS-TOP-21-014

CMS-PAS-TOP-21-014
Measurement of the $\mathrm{t\bar{t}}$ charge asymmetry in highly boosted events in the single-lepton channel at 13 TeV
CMS Collaboration
May 2022

Abstract: The measurement of the charge asymmetry for highly boosted top quark pairs decaying to a single lepton and jets is presented. The analysis is performed using 138 fb $^{-1}$ of data collected in pp collisions at $\sqrt{s}=$ 13 TeV with the CMS detector during Run 2 of the Large Hadron Collider. The selection is optimized for top quark-antiquark pairs produced with large Lorentz boosts, resulting in non-isolated leptons and overlapping jets. The top quark charge asymmetry is measured for events with $\mathrm{t\bar{t}}$ invariant mass larger than 750 GeV and corrected for detector and acceptance effects using a binned maximum likelihood fit. The measured top quark charge asymmetry is in good agreement with the standard model prediction at next-to-next-to-leading order in perturbation theory with next-to-leading order electroweak corrections. Differential distributions for two invariant mass ranges are also presented.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 846 (2023) 137703. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$ +jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta \|y\|$ (top left), reconstructed ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.
png pdf	Figure 1-a: Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$ +jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta \|y\|$ (top left), reconstructed ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.
png pdf	Figure 1-b: Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$ +jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta \|y\|$ (top left), reconstructed ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.
png pdf	Figure 1-c: Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$ +jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta \|y\|$ (top left), reconstructed ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.
png pdf	Figure 1-d: Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$ +jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta \|y\|$ (top left), reconstructed ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.
png pdf	Figure 2: Comparison between data and SM prediction for ${\Delta \|y\|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $\le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le$ 900 GeV, and the plots in the bottom row to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} >$ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.
png pdf	Figure 2-a: Comparison between data and SM prediction for ${\Delta \|y\|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $\le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le$ 900 GeV, and the plots in the bottom row to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} >$ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.
png pdf	Figure 2-b: Comparison between data and SM prediction for ${\Delta \|y\|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $\le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le$ 900 GeV, and the plots in the bottom row to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} >$ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.
png pdf	Figure 2-c: Comparison between data and SM prediction for ${\Delta \|y\|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $\le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le$ 900 GeV, and the plots in the bottom row to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} >$ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.
png pdf	Figure 2-d: Comparison between data and SM prediction for ${\Delta \|y\|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $\le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le$ 900 GeV, and the plots in the bottom row to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} >$ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.
png pdf	Figure 3: The measured ${A_{C}}$ values in different mass regions, combining the $\mu$ +jets and e+jets channels, compared with the prediction in the fiducial region obtained by fitting Asimov data (left) and the theoretical prediction including NNLO QCD and NLO EW corrections from Ref. [4] (right).
png pdf	Figure 3-a: The measured ${A_{C}}$ values in different mass regions, combining the $\mu$ +jets and e+jets channels, compared with the prediction in the fiducial region obtained by fitting Asimov data (left) and the theoretical prediction including NNLO QCD and NLO EW corrections from Ref. [4] (right).
png pdf	Figure 3-b: The measured ${A_{C}}$ values in different mass regions, combining the $\mu$ +jets and e+jets channels, compared with the prediction in the fiducial region obtained by fitting Asimov data (left) and the theoretical prediction including NNLO QCD and NLO EW corrections from Ref. [4] (right).
png pdf	Figure 4: The impacts of the nuisance parameters corresponding to the systematic uncertainties for the inclusive ${A_{C}}$ measurement for ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \ge$ 750 GeV. The blue and red bars show the effect on the unfolded ${A_{C}}$ values for up and down variations of the systematic uncertainty. MC statistical uncertainties are omitted here.

Tables
png pdf	Table 1: Event yields after the likelihood fit for each of the 12 channels used in the analysis ( $\mu$ +jets, e+jets and 3 years: 2018, 2017, and 2016), separated into the two mass regions, for events that pass the signal sample selection. The errors shown include both the MC statistical and the total systematic uncertainty.
png pdf	Table 2: Measured unfolded charge asymmetry at fiducial phase level in individual channels compared with the SM predictions.

Summary

The first measurement of the charge asymmetry for highly boosted top quark-antiquark pairs in pp collisions at

$\sqrt{s} =$ 13 TeV has been presented based on 138 fb

$^{-1}$ of data. The selection was optimized for top quark-antiquark pairs produced with large Lorentz boosts and decaying to a single lepton + jets, resulting in non-isolated leptons and overlapping jets. The top quark charge asymmetry is corrected for detector and acceptance effects using a binned maximum likelihood fit. The resulting unfolded charge asymmetry for

$\mathrm{t\bar{t}}$ events with

${M_{\mathrm{t\bar{t}}}} \ge$ 750 GeV corrected to the full phase space is

${{A_{C}} ^{\text{full}}} =$ 0.0069

$_{-0.0069}^{+0.0065}$ . The corresponding theoretical prediction at NNLO in perturbation theory with NLO electroweak corrections from Ref. [4] is 0.0094

$^{+0.0005}_{-0.0007}$ . Good agreement between the data and the SM prediction is observed.

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